Enhancing effect of tuberculin allergy as a result of repeat tests with 1 TU RT 23 on groups tested with I TU, 20 TU and placebo was studied by random allocation among population not vaccinated with BCG in 8 villages. In all, 2357 persons were tested with 1 TU and 759 with normal saline at first round. Based on testing at three rounds the study population could be divided into eight different groups and were labelled with alphabets 'a' to 'h' having been tested once, twice or thrice. The groups 'a', 'c', 'e' & ’g' were tested at 2 months, round two with 1 TU RT 23 and remaining half were not tested. However, all available persons in the 8 groups were retested at the third round, 18 months after the initial test. Thus, eight groups cannot be treated as independent samples but representative of the whole population.

The study did not show enhancing effect due to previous tuberculin test with 1 TU alone among groups tested once, twice or thrice after an interval of 18 months. Part of population was tested with 20 TU at round one; boosting effect was seen at 2 months when test was repeated. However, it was not seen after 18 months but when exactly the boosting effect disappeared was not known. Thus, there was no increase in reaction even among those who were tested with a higher dose of 20 TU earlier after 18 months. The groups provided the largest number for comparison between tested and the control groups. It is inferred from the study that boosting with high dose or repeat tests with the same dose does not persist after 18 months. Hence, for classifying positive tuberculin reactors, no correction is required to the same individuals/population after an interval of 18 months or more, as no boosting effect after 18 months has been observed, on the basis of this analysis.

The National Tuberculosis Control Programme is in operation since 1962, and its quantitative achievement is being monitored indirectly through records and reports received from District Tuberculosis Centres. For direct evidence of impact of the programme, tuberculin surveys are useful in reflecting the recent epidemiological situations prevailing in the area. Tuberculosis being a disease of secular nature, a periodic follow up with five years (arbitrary) interval may be preferred over the continuous follow up, for finding the trend of tuberculosis situations in an area.

Keeping in view the importance of tuberculin surveys, National TB Institute (NTI) has evolved a surveillance system which can be adopted by any state in India. The state teams can be trained at NTI in registering population, tuberculin testing & reading, so as to carry out the surveillance in their respective areas. It is essential to create a central organisation for surveillance of tuberculosis using the tuberculin test. The centre would be responsible for technical & administrative support and monitoring. NTI could provide technical expertise in formulating the surveillance system, a training methodology and an in service training to the designated staff.

A methodology in brief about conducting Classical Tuberculosis Sample Survey and Tuberculosis Surveillance is given below:

I. CLASSICAL TUBERCULOSIS SAMPLE SURVEY
A tuberculosis prevalence survey to measure the problem of tuberculosis in the community is a challenging assignment especially so when it is to be conducted by an organisation not created with the specific objectives of carrying out research work e.g., the District Tuberculosis Centre, State Tuberculosis Centre, etc. However, following procedure is described in brief: (1) Selection of district for the study, (2) Collection of basic data like size and distribution of population, number of towns and villages, (3) Selection of sample population for survey by valid statistical methods, (4) Census enumeration of study population by trained census takers - preparation of cards for all the individuals, (5) Tuberculin testing & reading of all subjects under study, (6) BCG scar survey, (7) X- ray examination of the eligible population (> 10 years or > 15 years). Interpretation of X-rays by standard readers, (8) Collection of sputum from chest symptomatics and X-ray abnormal individuals, (9) Transportation of sputum to central laboratory (necessary precaution to be taken during storing and transportation), (10) Sputum to be examined by trained staff, (11) Compilation, analysis and interpretation of data. Number of working teams with full complement of staff depends upon the size of the study population and the time frame of the study. An average survey team may have the following personnel on its strength: Medical Officer - One, Census Takers - Three, Tuberculin Tester & Reader (one each) - Two, Lab Technician - One, Lab Asst. - One, X-ray Technician. - One, Dark room attender - One. Equipment required: Mobile X-ray unit - mounted on a jeep along with the generator mounted on another jeep, Laboratory infrastructure, Vehicles preferably jeep.

Apart from the above, the team may need part time assistance of a Statistician and a few Statistical Computers. In case a state is interested to carry out an epidemiological survey, it may need to create the above infrastructure. Once arranged, it may request the National TB Institute (NTI) to train the required staff on standard survey techniques under field situations which is very essential.

II. TUBERCULOSIS SURVEILLANCE
In contrast to the more complex methodology involved in a classical survey described above, an alternative, much simpler and indirect method to assess the problem of tuberculosis in the community is by finding out the infection rate, through tuberculin surveys. It may be possible to estimate the prevalence of sputum smear positive disease from infection rate. Such survey is conducted by subjecting the age-specific unvaccinated population to tuberculin test periodically. For carrying out the work, one to two teams composed of three to four properly trained tuberculin testers and readers are needed along with at least two vehicles and a standby vehicle per team. Budgetary support for petrol, travelling and daily allowance of staff, and for minor miscellaneous expenditure like stationery, spirit, etc., may be required to be provided. Training could be imparted to such personnel at NTI and their services utilised exclusively for carrying out tuberculin surveys as a regular ongoing surveillance activity. If this methodology is found suitable, one may take action to create posts of tuberculin testers and readers in suitable scales and draft them for training in tuberculin survey methodology. The Institute will be happy to train the required personnel for the purpose, as well as analyse the data so collected for use by the states.

A study was conducted in 1983-84 by the National TB Institute (NTI) in the districts of Dharmapuri (Tamil Nadu) & Ananthapur (Andhra Pradesh). Thirteen health personnel were trained in census taking, tuberculin testing & reading and data keeping etc., at the NTI according to the standard methodology. The trainees were repeatedly assessed and only those who achieved a reasonably high inter-reader correlation with the standard reader were chosen for the field work. Field work was carried out by these health workers and supervised by the team leaders of NTI. Children between 0-9 years were tested with 1 TU RT 23 with Tween 80 in tuberculin testing centres specially set up in each village and the reactions were read between 48 & 72 hours after the test. The tuberculin testing/reading coverage was very high. Of 6702 eligible children, 5904 (97%) were tuberculin test read.

Individual reading assessment carried out at Ananthapur and Dharmapuri for the State Field Workers (SFWs) showed that agreement with Standard Reader (SR) of NTI at three induration levels i.e., 10+ mm, 14+ mm and 18+ mm were very high. The demarcation line between infected and uninfected appeared to be about 18 mm. In Ananthapur, the agreement at 18+ mm was 99% and at Dharmapuri it was 100% for SFW, and 98.4% for SFW-2. The estimates of prevalence rate of infection were 9.3% - SFW V/s 9.7% - SR at Anantapur, 5.2% - SFW V/s 5.2% - SR and 7.2% - SFW.2 V/s 7.2% - SR at Dharmapuri. The study further showed that it was possible to train general health workers, within a period of 3 months to attain a high level of efficiency. The general health services can successfully organise on their own a programme of tuberculin testing in the community with proper liaison and supervision by some nodal agency. The training and field supervision responsibilities may be shouldered initially by NTI or another suitable organisation, till these nodal agencies come up.

To obtain precise information for computing the indices of tuberculosis situation in a community, with passage of time, reliance has been placed on tuberculosis infection rates obtained by carrying out tuberculin surveys. In most developing countries, covered extensively by BCG vaccination without prior tuberculin testing, the tuberculin test has problems of interpretation for demarcating the infected persons from the uninfected. To overcome the problem, therefore, the test results are analysed among persons who do not show a BCG scar and are, thus, considered as normal population. In this paper, an attempt is made to show that BCG vaccination not always lead to the formation of a scar, and also that the scar resulting from BCG vaccination may fade away with time and the person, thus, may be wrongly included in the unvaccinated group. It has also been found that there is greater fading of scars in the younger age groups: in children 0-2 years of age, upto 52% of the scars faded away within 21 months of vaccination. This proportion steadily decreased to about 8% in the 10-14 years age group.
The implication of the finding is that the demarcation line between uninfected and infected persons may require to be shifted from survey to survey, based on the distributions among the 'no scar' population. Moreover, in a totally vaccinated community, the differences of reactions may provide the answer to the problem of identifying the newly infected persons.

The purpose of this investigation was to compare the corresponding longitudinal and transverse diameters of tuberculin test and study the influence of reader variations, size of reaction and the age specific infection rates, in order to understand the effect of switching over from the transverse to longitudinal readings. The study was carried out in villages in south India where no BCG or tuberculin testing had been undertaken. A total of 1240 persons were given tuberculin test with 1 TU RT 23 in both longitudinal and horizontal diameters. The indurations were read after 2-4 days by two readers independently. The study showed that though the longitudinal diameters were bigger than the corresponding transverse diameters, these differences did not influence infection rates calculated at 10 mm or more induration level. In National Tuberculosis Institute (NTI), Bangalore the practice of reading transverse diameter was altered to longitudinal diameter in the epidemiological surveys as it was comparatively easier to read the longitudinal diameter. Obtaining almost similar infection rates at the 10 mm or more level of induration in this study, irrespective of readers and diameters has minimized the effect of the changeover from transverse to longitudinal diameter reading in the epidemiological surveys at NTI. This would also not pose any problem in comparing the results of NTI studies with other research studies by any national or international organisation where transverse diameters have been measured.